Electronic structure of the lead monoxides: Band-structure calculations and photoelectron spectra

PbO is a layer compound which exists in two polymorphic forms, a red tetragonal (α) and a yellow orthorhombic (β) modification. Ab initio band-structure calculations are presented for both phases. The calculated energy gaps are in agreement with optical data. The band-structure calculations are used to discuss the chemical bonding in the α and β phases. It is found that the Pb 6s states are strongly hybridized with O 2p orbitals. Thus the so-called Pb (6s${)}^2$ lone pair in PbO takes part in the chemical bonding, and cannot be considered as an inert pair. Photoelectron spectra of the valence band and of some core levels are presented for α- and β-PbO. The observed valence band is in good agreement with the calculated band structure.